Many paperboard folders have been conventionally made having a one piece construction formed to have a front panel a rear panel and optionally a pocket at a lower front portion of the rear panel. Such folders are used to assemble various printed materials in a convenient package format. It is also known to include binding apparatus for retaining sheet material as part of the folder either permanently or releasably between the front and rear panels. Conventional folders are frequently constructed of like cardboard or bristol board in order to provide a degree of protection for the bound sheet material.
Since it is desirable to provide printed material on the exterior of the front or rear panels, known paperboard folders include two piece folders in which the front and rear panels are separable to facilitate printing on standard photocopying or offset printing equipment without the need for large printing machinery required to print one piece folders. Such two piece folders are described in my U.S. Pat. Nos. 5,025,978 granted Jun. 25, 1991 and 5,104,250 granted Apr. 14, 1992.
The two piece folders of the patents are most advantageous for use as relatively simple paperboard folders to hold a minimal amount of sheets. The folders suffer from disadvantages associated with adhesives used to bind the elements together. One disadvantage is that the binder cannot practically be disassembled after being secured by the adhesive. Further such adhesives perform admirably when used with relatively simple folders however have some disadvantages when the folder is intended to have separable binder means to hold a large number of sheets. The weight of the sheets on the binder can be considerable. When used with a large number of sheets, the more widely spaced paperboard covers come to be placed under great loading in use on their edges and fold lines. In such an application a paperboard cover does not protect the enclosed sheets as well as in an application where such covers are closely spaced in a folder containing only a few sheets.
Of course, known three ring binders are known in which a substantial, one piece member of rigid vinyl covered cardboard forms the cover.
Such three ring binders suffer the disadvantages that they can not easily be printed and that their ring binders are applied to the cover with machinery.
The prior art suffers the disadvantage that folders are not known which have strength to advantageously protect a number of sheets secured in a binder yet can readily be printed by smaller printing establishments.